Those who crusade against illegal immigration – claiming that cheap labor depresses wages and hurts low-skilled American workers – like to talk about the economic impact.

Americans would have a better debate if we started accepting some undeniable economic realities.

Undeniable Reality No. 1: Guest worker programs often don’t work as advertised. Workers are often exploited because employers tend to conclude that trying to ensure otherwise – through fair wages, housing, etc. – trims profits. Once that happens, employers lose interest in the program and look elsewhere for labor.

Undeniable Reality No. 2: Illegal immigrants don’t depress wages; employers do. I’m sure immigrants would love to take home more pay every week, but they don’t have the power to make that happen.

One complaint can get them fired.

Undeniable Reality No. 3: The idea that illegal immigrants will “self-deport” if you dry up all the jobs isn’t realistic.

What do immigrants have to go home to? The self-deport argument is simply a cop-out for those who don’t have the will to deport millions of illegal immigrants or give them amnesty.

Undeniable Reality No. 4: There will always be jobs for illegal immigrants because many Americans want to enjoy upper-class luxuries on middle- class salaries. Like the man who called in to a radio show I was on and volunteered that – as a single parent – he had hired an illegal immigrant to baby-sit his kids while he worked. The caller said he paid the nanny about $6 per hour, but that hiring a U.S. citizen might cost him twice as much. Multiply this guy by millions and you start to get the picture.

Undeniable Reality No. 5: We all benefit from illegal immigration. Even if you don’t benefit directly – like that single parent – chances are you benefit indirectly by enjoying the fruits of a robust economy or lower prices on goods and services. From Phoenix to Denver to Charlotte to Las Vegas, U.S. cities with high concentrations of illegal immigrants are enjoying construction booms and thriving economies. At the other extreme, economically depressed states such as West Virginia have – according to surveys – very few illegal immigrants.

Undeniable Reality No. 6: Mexican workers are going to continue to come to the United States – legally if possible, illegally if necessary – as long as they can earn 15 to 20 times more in this country than they can back home. In many villages in Mexico, workers might earn just $3 to $6 per day. In the United States, they might earn $60 per day for farm work or $90 per day for construction work. What would you be willing to do to make 20 times what you make now?

Undeniable Reality No. 7: When you’re talking about employers and workers, and the workers are here illegally, the laws of supply and demand fall apart. After a speech at a college in southern Indiana, an economics professor suggested that one way to force farmers in Mexico to pay higher wages was to encourage more immigration from that country. The logic seemed to be that if you further drain off the labor supply, you’d force employers in Mexico to raise their wages. By extension, the same sort of pressure could be applied to manipulate the behavior of U.S. farmers.

Not so fast. What the professor was talking about was white-collar economics. From her vantage point, if another college wanted to lure her away and offered to increase her salary by 20 percent, then the college she’s at now would be forced to increase her pay by at least as much to keep her on staff. That’s generally how it works in the white-collar world.

But the professor could use a quick tutorial in Farm Economics 101. Her theory involved low-skilled farm workers – people who perhaps can’t read or write, who usually have limited skills, who can’t defend themselves against unscrupulous employers and who are easily replaced, on either side of the border. These people are at the bottom of the economic food chain and they don’t have any leverage. There’s a wide chasm between such workers and their employers – socially, economically and culturally – and it makes it difficult for those workers to ever earn the respect they deserve.

If American farmers are squeezed with labor shortages, they’ll simply do what they have done for decades – intensify their demands on Congress for more guest workers from other countries.